1. Field of the Invention
The present invention relates generally to the art of reclosable plastic bags having extruded zippers, and more particularly to the provision of the fastener profiles on such bags with a member comprising a low-melting-point or high-flow polymeric material, said member providing a caulking means at the side seals thereof.
2. Description of the Prior Art
Reclosable bags used, for example, for storing household foodstuffs are typically made of polyethylene. As shown in U.S. Pat. No. 3,416,199 to Imamura, a reclosable bag may be formed of two opposed walls equipped at the mouth with fastener profiles. These profiles include a male profile attached to one wall and a female profile on the other wall. The profiles are shaped so that, when they are aligned and pressed together into an engaging relationship, they form a continuous closure for the bag. The bag may be opened by pulling the walls apart to separate the profiles.
In general, the profiles are designed to provide relatively high resistance to opening from inside the bag while rendering the bag relatively easy to open from the outside. For example, U.S. Pat. No. 5,368,394 to Scott et al. discloses a reclosable bag formed of walls defining a closure with a mouth. The closure includes an asymmetric arrowhead male profile extending along an internal surface of one of the walls and a female profile having stubs adapted to interengage with the male profile and extending along an internal surface of the other wall. Both profiles also include stabilizer wedges on both sides thereof and parallel thereto across the width of the bag. The stabilizer wedges give the zipper formed by the male and female profiles a wide-track feel, and help determine the force required to open the bag both from inside and from outside.
In general, the interlocking zipper profiles for reclosable plastic bags are extruded from low density polyethylene (LDPE). These zipper profiles are usually attached to the polymeric sheet material, from which bags or packages are being produced, on a form-fill-and-seal (FFS) machine, although the zipper profiles may be integrally extruded with the polymeric sheet material.
While most FFS machines are of several specific designs, all comprise a filling tube, about which the bags or packages are formed and through which premeasured amounts of a consumer product, such as a food material, may drop as individual bags or packages are being produced in a sequential fashion. On the FFS machine, polymeric sheet material is directed toward and around the filling tube by means of a forming collar, the two lateral edges thereof being brought together to form a fin extending outward from and longitudinally along the filling tube. The male and female interlocking zipper profiles are usually directed between the two lateral edges and are joined or heat-sealed thereto to form the facing inner portions of the reclosable bag opening.
As bags or packages are being produced and filled in a sequential fashion on an FFS machine, seals are made transversely across the polymeric sheet material and interlocked male and female zipper profiles to form the side seals of individual packages. Because of the bulk of the zipper profiles relative to that of the polymeric sheet material, the zipper profiles require some pre-seal treatment in the location where a side seal is to be made, so that the side seal may be complete and not permit any leakage of the contents of the package. Such pre-seal treatment may include the use of heat stompers (hot anvils which crush the zipper profiles at the location of the side seal to be subsequently made), ultrasonic welders (similar to heat stompers but employing ultrasonic energy), hole punchers (which remove a portion of the zipper profile where the side seal is to be applied), and milling cutters (which abrade away a portion of the zipper profile at the side seal location). The pre-seal treatment permits the cross sealing equipment to make a reasonable seal. Unfortunately, such pre-seal treatment of the zipper profiles does not entirely eliminate the occurrence of leaking packages, or "leakers" and complicates the FFS machine.
The present invention is intended to reduce or eliminate the occurrence of "leakers" by providing at least one of the two profiles being joined with a low-melting-point or high-flow member, which is readily melted when the side seal is being made and which in liquid form flows into and caulks any openings remaining after the zipper profiles have been flattened.